Fukushima Nuclear Accident Update Log
Updates of 26 April 2011
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- In Focus: Fukushima Nuclear Accident
- Fukushima Nuclear Accident: Information Sheet
- Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency
- International Nuclear and Radiological Event Scale (INES)
- IAEA Incident and Emergency Centre (IEC)
- International Seismic Safety Centre (ISSC)
- Response Assistance Network (RANET)
- Japan Nuclear and Industrial Safety Agency (NISA)
IAEA Briefing on Fukushima Nuclear Accident (26 April 2011, 18:00 UTC)
→ Summary of Reactor Status
1. Current situation
Overall, the situation at the Fukushima Daiichi nuclear power plant remains very serious, but there are signs of recovery in some functions, such as electrical power and instrumentation.
After the announcement on 11 April by the Government of Japan to establish 'planned evacuation zones' and 'emergency evacuation preparation zones', in a press conference on 22 April by the chief cabinet secretary of Japan Mr. Edano it was stated that "the Prime Minister, as head of the Nuclear Emergency Response Headquarters, has issued instructions to the governor of Fukushima Prefecture and the heads of municipal governments concerned." These instructions included:
- Designation of 'planned evacuation zones' to be applied to some specific zones outside the 20 km radius from the Fukushima Dai-ichi plant: "the villages of Katsurao, Namie and Iitate, part of the town of Kawamata, and part of the city of Minamisoma", where planned evacuations are expected to be implemented in approximately one month's time.
- Designation of 'emergency evacuation preparation zones', to be applied to the area within a 20-30 km radius from the Fukushima Dai-ichi plant (except for areas designated as planned evacuation zones): "the towns of Hirono and Naraha, the village of Kawauchi, and parts of the cities of Tamura and Minamisoma", in which preparations should be made so that the residents can take shelter indoors or can evacuate by their own means in the event of an emergency. In addition, with regard to the areas located within a 20-30 km radius from the nuclear power plant, the advisory for sheltering indoors that has been in effect to date has been lifted.
Changes to Fukushima Daiichi plant status
The IAEA receives information from various official sources in Japan through the Japanese national competent authority, the Nuclear and Industrial Safety Agency (NISA). Additional detail is provided in the IAEA Incident and Emergency Centre (IEC) status summary with information received by 07:00 UTC on 26 April 2011.
Management of on-site contaminated water
According to the 25 April evaluation by NISA of the report submitted by TEPCO, there is a little less than 70,000 tonnes of stagnant water with high level radioactivity in the basement of the turbine buildings of Units 1, 2 and 3.
On 25 April the power supply for the temporary electrical pumps that supply water to the reactor pressure vessel of Units 1, 2 and 3 was switched from the off-site power supply to temporary diesel generators to allow work to enhance the off-site supply.
White smoke continues to be emitted from Units 2, 3 and 4.
In Unit 1 fresh water is being continuously injected into the reactor pressure vessel through the feedwater line at an indicated flow rate of 6 m3/h using a temporary electric pump with off-site power.
In Unit 2 and Unit 3 fresh water is being continuously injected into the reactor pressure vessel through the fire extinguisher line at an indicated rate of 7 m3/h using temporary electric pumps with off-site power.
In Unit 4 140 tonnes of fresh water was sprayed over the spent fuel pool on 23 April and 165 tonnes of fresh water was sprayed over the spent fuel pool on 24 April using a concrete pump truck. The nuclear emergency response headquarters reported that temperature measurements showed the spent fuel pool temperature to be 83 °C before spraying and 66 °C after spraying on 23 April, and the spent fuel pool temperature to be 86 °C before spraying and 81 °C after spraying on 24 April.
Nitrogen gas is being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion in the containment vessel. The pressure in the reactor pressure vessel is increasing.
The reactor pressure vessel temperatures in Unit 1 remain above cold shutdown conditions. The indicated temperature at the feedwater nozzle of the reactor pressure vessel is 138 °C and at the bottom of reactor pressure vessel is 111 °C.
The reactor pressure vessel temperatures in Unit 2 remain above cold shutdown conditions. The indicated temperature at the feed water nozzle of the reactor pressure vessel is 123 °C. The reactor pressure vessel and the dry well remain at atmospheric pressure. Fresh water injection (approximately 38 tonnes) to the spent fuel pool via the spent fuel pool cooling line was carried out on 25 April.
The temperature at the bottom of the reactor pressure vessel in Unit 3 remains above cold shutdown conditions. The indicated temperature at the feed water nozzle of the reactor pressure vessel is 75 °C and at the bottom of the reactor pressure vessel is 111 °C. The reactor pressure vessel and the dry well remain at atmospheric pressure.
There has been no change in the status in Unit 5 or Unit 6 or in the common spent fuel storage facility.
2. Radiation monitoring
For the period 21-25 April deposition of I-131 was detected in eight prefectures, ranging from 2.2 to 37 Bq/m2. Deposition of Cs-137 was detected in 11 prefectures, the values reported ranging from 1.3 to 69 Bq/m2.
Gamma dose rates are measured daily in all 47 prefectures. For Fukushima prefecture gamma dose rates decreased from 1.9 μSv/h on 21 April to 1.7 μSv/h on 23 April. In Ibaraki prefecture, gamma dose rates were 0.12 μSv/h. In all other prefectures, reported gamma dose rates were below 0.1 μSv/h with similar decreasing trends.
Gamma dose rates reported specifically for the eastern part of Fukushima prefecture, for distances beyond 30 km from Fukushima Dai-ichi, showed a similar general decreasing tendency, ranging from 0.1 to 19.4 μSv/h on 25 April. The latest maximum reported value for 20 April was 24 μSv/h.
The other 45 prefectures presented gamma dose rates of below 0.1 μSv/h, falling within the local natural background range.
In drinking water, I-131 or Cs-137 is detectable, but in only a few prefectures. As of 1 April, the one remaining restriction on the consumption of drinking water relating to I-131 (at a level of 100 Bq/L) applies to only one village in the Fukushima prefecture, and the restriction applies only to infants.
Food monitoring data were reported by the Japanese Ministry of Health, Labour and Welfare on 21 April for a total of 62 samples taken over 18-21 April from 11 prefectures (Chiba, Fukushima, Gunma, Ibaraki, Kanagawa, Nagano, Niigata, Saitama, Tochigi, Tokyo and Yamagata). Analytical results for all of the samples of various vegetables, mushrooms, seafood and unprocessed raw milk indicated that I-131, Cs-134 and Cs-137 were either not detected or were below the regulation values set by the Japanese authorities.
Food monitoring data were reported by the Japanese Ministry of Health, Labour and Welfare on 22, 23 and 24 April for a total of 164 samples taken in the period 19-23 April from 11 prefectures (Chiba, Fukushima, Gifu, Gunma, Hyogo, Ibaraki, Kanagawa, Niigata, Saitama, Tochigi and Yamagata). Analytical results for 158 of the 164 samples of various vegetables, mushrooms, fruit (strawberry), seafood and raw unprocessed milk indicated that I-131, Cs-134 and Cs-137 were either not detected or were below the regulation values set by the Japanese authorities. Six samples of shiitake mushrooms (grown outdoors) taken in Fukushima prefecture on 21 April were above the regulation values set by the Japanese authorities for Cs-134/Cs-137.
Food monitoring data were reported by the Japanese Ministry of Health, Labour and Welfare on 25 April for a total of 15 samples taken on 21 and 24-25 April from seven prefectures (Fukushima, Gunma, Ibaraki, Kanagawa, Niigata, Tochigi and Yamagata). Analytical results for all of the samples of various vegetables, fruit (strawberry), beef, milk and raw unprocessed milk indicated that I-131, Cs-134 and Cs-137 were either not detected or were below the regulation values set by the Japanese authorities.
On 21 April restrictions on the distribution of raw unprocessed milk produced in Soma City and Shinchi town in Fukushima prefecture were lifted, as well as the restriction on the distribution of spinach from Nasushiobara City and Shioya town in Tochigi prefecture. On 22 April, the restrictions on the distribution of spinach, shungiku, qing-geng-cai, sanchu, celery and parsley produced in Chiba prefecture were also lifted.
On 22 April the chief cabinet secretary Mr. Edano announced that "a decision has been made to prohibit the cultivation of rice for the duration of the 2011 harvest within the evacuation zones, planned evacuation zones and emergency evacuation preparation zones", in Fukushima prefecture (http://www.kantei.go.jp/foreign/incident/110422_0944.html). This measure concerns rice grown for human consumption on the land most affected by the deposition of radionuclides.
On 25 April in Fukushima prefecture restrictions on the distribution of shiitake mushrooms produced in Iwaki City were lifted. Restrictions were placed on the distribution of shiitake mushrooms from Motomiya City.
3. Marine monitoring
Marine monitoring programmes
Further to previous briefings, new monitoring points have been announced by TEPCO, with sampling starting 25 April. FIG. 1 shows existing and new TEPCO sampling points, as well as existing and new MEXT sampling points.
The Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) added further sampling points in its off-shore monitoring programme on 25 April (see FIG. 1). In addition, sampling has started (on 25 April) in five off-shore points off Ibaraki Prefecture.
FIG. 1. TEPCO and MEXT sea water sampling locations.
Monitoring at off-shore sampling points consists of:
- Measurement of ambient dose rate in air above the sea;
- Analysis of ambient dust above the sea;
- Analysis of surface samples of sea water;
- Analysis of samples of sea water collected at 10 m above the sea bottom.
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